Polyurethane polymers, especially foams, with improved mechanical properties (particularly tensile strength and hardness) can be prepared by reacting an organic polyisocyanate with a polyahl composition where at least one component comprises a stable dispersion.
Typically the dispersion consists of a polyurea or polyhydrazo-dicarbonamide which is prepared by reacting a diisocyanate with difunctional primary or secondary amines, hydrazines or hydrazides in polypropylene glycol ethers. Such processes are described in the literature in, for example, U.S. Pat. Nos. 3,325,421 and 4,089,835, German Patent DE 2,513,815 and are extensively reviewed by K. G. Spitler and J. J. Lindsey, Journal of Cellular Plastics, Vol. 17, p. 43 (1981). Complementary to these dispersions are those polyisocyanate-derived polyurea dispersions in aromatic polyisocyanates such as disclosed by patent GB 2,127,031.
To date, all polyurea dispersions in either polyether polyols or organic polyisocyanates involve the handling of organic polyisoeyanates in the preparation of the particulate matter of such dispersions. Polyisocyanates are relatively expensive starting materials and also toxic compounds which have to be handled with care.
Accordingly, it would be desirable to provide a process for the preparation of a stable polyurea dispersion which does not involve the use of an organic polyisocyanate. By stable, it is understood that the dispersion can be stored for an extended period, at least 2 weeks, preferably at least one month and up to 6 months, and subjected to normal fluctuations of room temperature without the dispersed particulate polymer agglomerating or solidifying to any significant degree, thus preventing its further use. Some sedimentation of the particulate solid may take place during storage, but this can readily be redispersed on agitation.
It is known that polyhydroxyalkyl monoureas can be synthesized by reacting urea with a polyhydroxylamine as already described in, for example, U.S. Pat. Nos. 3,560,564 and 4,546,121, German Patent 1,463,398, German Offenlegungsschrift 2,703,185 and British Patent 1,127,605. Such prepared monoureas, especially trishydroxyalkyl monoureas, are frequently liquids and form stable liquid dispersions in polyols at room temperature. These dispersions find value as reactive flame-proofing reagents in polyurethane foams.
It is therefore an objective of this invention to develop a discrete particulate polymer and polyahl compositions therewith for improving the mechanical properties of polymer matrices, especially those comprising urethane and/or urea linkages. A further objective is to provide a process for the preparation of such a discrete particulate polymer which does not require the use of an organic polyisocyanate.